Cooler tube for rotary kiln

ABSTRACT

An improved cooler tube structure for a rotary kiln is disclosed. In construction, the cooler tube includes combined means for lifting and conveying material exiting from the kiln through the cooler tube. This combined means is selectively positioned at a predetermined distance away from the material inlet opening into the cooler tube. The cooler tube further includes separate means for conveying material exiting from the kiln through the cooler tube substantially without lifting it. The separate means is advantageously positioned upstream of said combined lifting and conveying means in relation to the direction of material flow through the cooler tube.

United States Patent [191 Chri stiansen [451 Aug. 20, 1974 COOLER TUBEFOR ROTARY KILN [75] Inventor: Soren B.,Christiansen, Copenhagen,

Denmark [73] Assignee: F. L. Smidth & Co., Cresskill, NJ.

[22] Filed: Jan. 3, 1973 [21] Appl. No.: 320,764

[30] Foreign Application Priority Data Jan. 17, 1972 Great Britain2138/72 [52] US. Cl. 432/80 [51] Int. Cl. F27b 7/38 [58] Field of Search432/80 [56] References Cited UNITED STATES PATENTS 1,905,744 4/1933Parker 432/80 2,001,258 5/1937 Lindhard 432/80 3,547,418 12/1970 Jensen..432/80 Primary Examiner.lohn J. Camby Attorney, Agent, or Firm-Pennie& Edmonds [5 7] ABSTRACT An improved cooler tube structure for a rotarykiln is disclosed. In construction, the cooler tube includes combinedmeans for lifting and conveying material exiting from the kiln throughthe cooler tube. This combined means is selectively positioned at apredetermined distance away from the material inlet opening into thecooler tube. The cooler tube further includes separate means forconveying material exiting from the kiln through the cooler tubesubstantially without lifting it. The separate means is advantageouslypositioned upstream of said combined lifting and conveying means inrelation to the direction of material flow through the cooler tube.

16 Claims, 8 Drawing Figures COOLER TUBE FOR ROTARY KILN BACKGROUND OFTHE INVENTION v the rotary kiln by a supply chute.

Planetary cooler tubes may be inclined upward in a direction extendingfrom their inlet ends (i.e. toward the material inlet end of the kiln)or they may be inclined downward in a direction extending away fromtheir inlet ends. In the former construction the planetary cooler tubesare commonly known as uphill tubes; the latter construction beingcommonly referred to as downhill tubes. Commonly, each cooler tubecontains scoops, chains or other devices by which the material enteringthe tube from the kiln is urged toward its outlet end. Uphill anddownhill cooler tubes are wellknown and widely used, particularly forcooling cement clinker produced by burning cement raw materials in therotary kiln with which the cooler tubes are associated.

ln constructions of the type described lifting devices are commonlyinstalled in the tubes to create selected material flow patterns throughthe cooler tube such that the material and the cooling air flowingthrough the tube in a direction countercurrent to the direction ofmaterial flow are brought into heat exchange relationship therebyadvantageously obtaining improved cooling of the material. In one knownconstruction such lifters are formed as trough-shaped conveyor flightsextending helically along the inner wall of each cooler tube from itsinlet to its outlet end. This type of lifter acts to lift the materialabove the horizontal plane through the axis of the tube and to dischargeit as cascading curtains of material which extend over substantially thewhole width of the tube at an inclined attitude with respect to the axisof the tube.

With constructions of the type described, the air flowing through eachcooler tube is heated for subsequent utilization in the kiln aspreheated secondary combustion air. It is advantageous from thestandpoint of overall economy of the kiln installation that asubstantial amount of the heat of the hot material entering the tubefrom the kiln be recovered and returned to the kiln with the secondarycombustion air. Effective heat exchange between the air and thecascading curtains of hot kiln material has been found to be valuable inachieving good heat recovery.

However, in cooler tube constructions of the type described thereisoften a tendency for some of the hot material that enters a givencooler tube when it is positioned below the axis of the kiln to returnto the kiln when the tube reaches a position above the axis, inasmuchas, when in the latter position, the outlets of the communicating chutesare, of course, positioned above their inlets.

By specially constructing the inlet end of each cooler tube to guide orconvey kiln material entering the tube away from its inlet end, thisreturn of material to the kiln may largely be prevented. However, insome circumstances, especially when the material treated is fine grainedor contains a large amount of dust particles, a substantial part of thiskind of material is entrained in the cooling air flowing through thecooler tubes and is thus carried toward the inlet ends of the coolertubes and ultimately back into the kiln. Dust particles and other finegrain material near the inlet ends of the cooler tubes is especially aptto be returned to the kiln in this'manner. Known means for guiding orconveying material away from the inlet ends of the cooler tubes havebeen found, in this case, to ineffectively prevent such material fromreturning to the kiln. Part of such material thus returns to the kilnand a substantial amount thereof may then circulate between the kiln andthe cooler tube so that the supply chute is constantly overloaded. Thisoverloading of the supply chute disadvantageously narrows the passagewayin the chute and undesirably restricts free flow of secondary combustionair from the cooler tubes to the kiln. A-further drawback resulting fromthe circulation of material between the kiln and the cooler tube is thatthe temperature of the material in the inlet end of the cooler tubebecomes so high that the temperature of the material discharged from thecooler tubes is above the acceptable temperature for dischargedmaterial. The higher material temperature also creates a highertemperature in the cooler tube proper, which may lead to a reduction inthe operating lift of parts of the cooler tube structure.

The present invention provides a new and unobvious cooler tube structurefor a rotary kiln which substantially prevents undesirable circulationof material between the kiln and the cooler tubes.

SUMMARY OF THE INVENTION In accordance with the present invention animproved planetary cooler tube structure is provided. In construction acooler tube according to this invention is provided with combinedmaterial lifting and conveying means extending helically along the innerwall of the cooler tube from a point axially spaced from the materialinlet end of the cooler tube by a distance equal to at least twice theinternal diameter of the cooler tube to a point located downstream ofsaid first mentioned point. Effective cooling of the material isperformed in this section of the cooler tube; the lifting and conveyingmeans acting to lift and drop the material so as to form cascadingcurtains through which the cooling air passes in heat exchangerelationship. With this construction, cooling is advantageouslyperformed at some distance from the inlet opening into the cooling tubeand, moreover, the disadvantage of the lifters throwing material uptoward the inlet opening of the cooler tube is avoided inasmuch asmaterial entrained by the cooling air as it passes through the cascadingcurtains of the material is largely precipitated from the air again asit passes through the section of the cooler tube having no lifters whichoccurs before the air passes through the communicating chute to thekiln.

A cooler tube according to this invention may also be equipped withseparate material conveying means. Advantageously, this separate meansmay be located upstream of the combined lifting and conveying means ormay be positioned to divide the said combined means into two parts. Thisseparate means, which may comprise screw thread-like protrusions orshallow throughs, acts to move the material to be cooled along the tubeaway from its inlet end substantially without lifting it.

The inlet end of a cooler tube according to this invention may also beequipped with a heat and wear resistent lining comprising plate-likeprotrusions covering the internal face of the cooler tube lining. Aninlet section of this type helps to prevent the backflow of materialinto the kiln, but at the same time, allows the cooling air to flowthrough the tube unrestricted by obstructions.

1 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation viewpartially in section of the outlet end of a rotary kiln provided withplanetary cooler tubes according to this invention;

FIG. 2 is a end view of the kiln shown in FIG. 1 as viewed from right toleft;

FIG. 3 is an enlarged longitudinal cross-sectional view of oneembodiment of a cooler tube constructed according to this invention;

FIG. 4 is a cross-sectional view taken along the line 44 in FIG. 3;

FIG. 5 is a cross-sectional view taken along the line 55 of FIG. 3;

FIG. 6 is a cross-sectional view taken along the line 6-6 of FIG. 3;

' FIG. 7 is a similar view to that shown in FIG. 3 but showing analternative embodiment of a cooler tube constructed according to thisinvention; and

FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show arotary kiln 1 with a refractory lining 2 for burning a charge 3 ofmaterial, for instance cement raw material, to clinker. In theconstruction shown in the drawings, the kiln is inclined downward towardits outlet end. The rotary kiln 1 has near its lower or outlet end anumber of outlet openings 4 which communicate via chutes 5 with acorresponding number of cooler tubes 6 arranged in planetary fashionequiangularly around the outlet end of the rotary kiln with their axesparallel to the axis of the kiln. Each chute 5 has a refractory liningl3 and the inlet end of each cooler tube has a heat-resistant lining l4.Inasmuch as the kiln is inclined downward, the cooler tubes 6 arecommonly known as uphill cooler tubes as will be readily appreciated bya person skilled in the art. It will also be recognized by personsskilled in the art that the rotational speed (i.e. the number ofrevolutions per minute) of the kiln is rather low which, in turn, meansthat the peripheral speed of the walls of the cooler tubes are alsoquite low.

The cooled material leaves each cooler tube through an outlet opening 7in the air inlet end of the tube. All the openings 7 are surrounded by astationary casing 8 the bottom of which is formed as a hopper 9 forcollecting cooled material leaving the cooler tubes. The cooled materialis discharged through a bottom opening 10 in the hopper.

As previously mentioned, in the construction shown in the drawings thecooler tubes mounted around the outlet end of the rotary kiln face orpoint uphill toward the inlet end of the kiln. It will be recognized, ofcourse, that the tubes may be arranged to point downhill away from theoutlet end of the kiln, and, particularly in large installations, thecooler tubes may be mounted separately from the kiln.

Asshown in FIG. 3, each cooler tube is provided with combined means forlifting and conveying material along the tube. This means comprisesconveyor flights 11 which are located in that end of the tube which isadjacent the outlet opening 7. Adjacent flights 11 on the inlet side oflifting flights 11 there are a series of troughs 12 which act only totransport material through the tube. The trough-shaped conveyor flights11 extend helically to the outlet end of the tube from a point spacedfrom the material inlet opening into the tube (i.e. the passagewaydefined by chute 5) by a distance equal to at least twice the internaldiameter of the tube. Advantageously, the distance between the upstreamend of the conveyor flights 11 (relative to material flow through thetube) and the material inlet opening can be at least equal to five timesthe internal diameter of the tube. The conveyor flights lift thematerial above the horizontal plane through the axis of the tube and inthe course of rotation discharge it again in the form of cascadingcurtains 15 depicted in FIG. 5. The curtains 15 are inclined to the axisof the tube and cover the crosssection of the tube completely so thatpassage of the cooling air through the tube is somewhat impeded.Thereby, effective heat exchange between the material and the coolingair takes place. It is to be noted that lifting conveyor flights 11serve not only to produce the curtains, but also to convey the materialtoward the air inlet end ofthe tube.

It is important to convey the material away from the air outlet end ofthe tube (i.e. the material inlet end) so that the material is unable tofall back into the kiln during rotation of the cooler tubes. Separateconveying means comprising screw thread-like troughs l2 posi tioned nearthe material inlet end of the tube effectively serve this purpose. Thesetroughs do not lift the material to any appreciable extent but ratherthey act to push it forward through the tube away from the air outlet ormaterial inlet end. i

It is important that material be transported and not significantlylifted by the protrusions or troughs 12. In order to ensure this, theangle of pitch of each trough 12 is greater than the angle of repose ofthe material. The angle of repose of the material treated in a kiln ofthe type shown in the drawings varies within certain limits. Forexample, with mineral products, say cement clinker, the angle of reposeis below 40 degrees. Thus, for applications involving mineral productsthe trace of the transporting devices or troughs 12 on the internal wallof the tubes should, according to this invention, form an angle with thegeneratrix of the tube of at least 40 degrees. With a pitch angle of thetransporting devices 12 determined according to this invention combinedwith the relatively low rotational speed of the kiln and low peripheralspeed of the cooler tube walls there is little chance thatmaterial inthe tube section containing the transporting devices will be lifted orwhirled-up to any undesirable extent.

Inasmuch as the material is not lifted into the air near the materialinlet end of the tube, the material is not to any significant extententrained in the air in this part of the cooler tube and, thus, thelikelihood of material being conveyed back into the kiln by the coolingair stream is substantially eliminated. Moreover, any mate rialentrained in the cooling air during its passage through the cascadingcurtains is advantageously precipitated out of the air stream in thissection of the tube with the result that only insignificant amounts ofmaterial are returned to the kiln with the cooling air.

The non-lifting material conveying means may take various structuralforms well known to persons skilled in the art. One form comprises thethroughs 12 shown in FIGS. 3 and 4 and previously mentioned. Anotherform comprises troughs 17 used in the embodiment of the invention shownin FIGS. 7 and 8 to be hereinafter described. The non-lifting conveyortroughs may form part of the cooler tube lining in which case thesetroughs may be composed of segments which permit easy repair ofreplacement of worn out parts.

Between the transporting troughs 12 and the material inlet end of thecooler tube the tube has a heat and wear-resistant lining defined by anuneven surface comprising plate sections 16. The uneven surface helps toprevent the back-flow of material into the kiln while simultaneouslyallowing the cooling air to flow through the tube substantiallyunrestricted by any appreciable obstructions which, were they to bepresent in the tube,

might-form eddy currents acting to carry material back into the kiln.The ultimate advantage of cooler tubes constructed according to thisinvention is that the velocity of the cooling air through the coolertubes, especially through the communicating chutes, is reduced and thecharge of material in the cooler tubes is kept relatively low. Thuscooling of the material is considerably improved.

FIG. 6 shows an alternative embodiment of a cooler tube constructedaccording to this invention. As shown therein, the non-lifting materialconveying or transporting means (i.e. troughs 17) are arranged in asection which divides the lifting flights 11 into two sections. Thisembodiment of the cooler tube has the same material inlet section asthat shown in the FIG. 3 embodiment.

I claim:

1. ln a rotary kiln having a plurality of cylindrical cooler tubesmounted in planetary fashion around the outlet end of the kiln with theaxes of the cooler tubes extending substantially parallel to the axis ofthe kiln, each cooler tube having a material inlet end and a supplychute connecting the material inlet end with the material outlet end ofthe kiln, the improvement wherein each cooler tube comprises a firstinlet section having a heat and wear resistant lining comprised ofplate-like sections which form an uneven surface extending axially alonga cylindrical portion of the tube, and a second section connected tosaid first section, said second section including combined materiallifting and conveying means extending helically along the inner wall ofthe cooler tube toward the outlet end of the cooler tube from a positionspaced axially from the material inlet end of the tube by a distance atleast equal to approximately twice the internal diameter of the coolertube.

2. The improved rotary kiln according to claim 1 wherein the distancebetween the upstream end of the combined lifting and conveying means inrelation to the direction of material flow through the tube and thematerial inlet end of the tube is equal to at least five times theinternal diameter of the tube.

3. The improved rotary kiln according to claim 1 wherein each coolertube includes separate means for moving material through the cooler tubesubstantially without lifting it.

4. The improved rotary kiln according to claim 3 wherein the combinedlifting and conveying means includes at least one through-shapedconveyor flight and wherein the separate means includes at least onescrew threadlike trough.

5. The improved rotary kiln according to claim 4 wherein each of saidtroughs is positioned between the inlet end of the cooler tube and thesection of the tube containing said conveyor flights.

6. The improved rotary kiln according to claim 4 wherein said troughsare positioned such that the conveyor flights are divided into twosections located on opposite sides of the tube section containing thecon- I veyor flights.

7. The improved rotary kiln according to claim 4 wherein the trace ofeach of said troughs on the internal wall of the tube forms an anglewith the generatrix of the tube which is greater than the angle ofrepose of the material in the cooler tube.

8. The improved rotary kiln according to claim 3 wherein said separatemeans is located upstream of said combined lifting and conveying meansin relation to the direction of material flow through the tube.

9. The improved rotary kiln according to claim 3 wherein said separatemeans is located within the tube such that said combined lifting andconveying means is divided into two sections disposed on oppositesidesof the section of the tube containing said separate means.

10. The improved rotary kiln according to claim 3 wherein said separatemeans includes at least one mateforms an angle with the generatrix ofthe tube which is greater than the angle of repose of the materialflowing through the tube.

11. The improved rotary kiln according to claim 8 wherein one section ofeach tube has a heat and wear resistant lining comprising plate-likesections forming an uneven surface.

12. The improved rotary kiln according to claim 11 wherein said separatemeans is located between said combined lifting and conveying means andsaid one section.

13. The improved rotary kiln according to claim .12 wherein said onesection is located adjacent the material inlet opening into the tube.

14. The improved rotary kiln according to claim 13 wherein said separatemeans, said combined means and said one section are located immediatelyadjacent each other along the length of the tube.

15. The improved rotary kiln according to claim 14 wherein said separatemeans includes at least one material conveying element mounted on theinterior wall of the tube such that the trace of said element on saidwall forms an angle with the generatrix of the tube which is greaterthan the angle of repose of the material flowing through the tube.

16. The improved rotary kiln according to claim 15 wherein said separatemeans, said combined means and said one section together extend oversubstantially the entire length of the tube.

1. In a rotary kiln having a plurality of cylindrical cooler tubesmounted in planetary fashion around the outlet end of the kiln with theaxes of the cooler tubes extending substantially parallel to the axis ofthe kiln, each cooler tube having a material inlet end and a supplychute connecting the material inlet end with the material outlet end ofthe kiln, the improvement wherein each cooler tube comprises a firstinlet section having a heat and wear resistant lining comprised ofplate-like sections which form an uneven surface extending axially alonga cylindrical portion of the tube, and a second section connected tosaid first section, said second section including combined materiallifting and conveying means extending helically along the inner wall ofthe cooler tube toward the outlet end of the cooler tube from a positionspaced axially from the material inlet end of the tube by a distance atleast equal to approximately twice the internal diameter of the coolertube.
 2. The improved rotary kiln according to claim 1 wherein thedistance between the upstream end of the combined lifting and conveyingmeans in relation to the direction of material flow through the tube andthe material inlet end of the tube is equal to at least five times theinternal diameter of the tube.
 3. The improved rotary kiln according toclaim 1 wherein each cooler tube includes separate means for movingmaterial through the cooler tube substantially without lifting it. 4.The improved rotary kiln according to claim 3 wherein the combinedlifting and conveying means includes at least one through-shapedconveyor flight and wherein the separate means includes at least onescrew threadlike trough.
 5. The improved rotary kiln according to claim4 wherein each of said troughs is positioned between the inlet end ofthe cooler tube and the section of the tube containing said conveyorflights.
 6. The improved rotary kiln according to claim 4 wherein saidtroughs are positioned such that the conveyor flights are divided intotwo sections located on opposite sides of the tube section containingthe conveyor flights.
 7. The improved rotary kiln according to claim 4wherein the trace of each of said troughs on the internal wall of thetube forms an angle with the generatrix of the tube which is greaterthan the angle of repose of the material in the cooler tube.
 8. Theimproved rotary kiln according to claim 3 wherein said separate means islocated upstream of said combined lifting and conveying means inrelation to the direction of material flow through the tube.
 9. Theimproved rotary kiln according to claim 3 wherein said separate means islocated within the tube such that said combined lifting and conveyingmeans is divided into two sections disposed on opposite sides of thesection of the tube containing said separate means.
 10. The improvedrotary kiln according to claim 3 wherein said separate means includes atleast one material conveying element mounted on the interior wall of thetube such that the trace of said element on said wall forms an anglewith the generatrix of the tube which is greater than the angle ofrepose of the material flowing through the tube.
 11. The improved rotarykiln according to claim 8 wherein one section of each tube has a heatand wear resistant lining comprising plate-like sections forming anuneven surface.
 12. The improved rotary kiln according to claim 11wherein said sepArate means is located between said combined lifting andconveying means and said one section.
 13. The improved rotary kilnaccording to claim 12 wherein said one section is located adjacent thematerial inlet opening into the tube.
 14. The improved rotary kilnaccording to claim 13 wherein said separate means, said combined meansand said one section are located immediately adjacent each other alongthe length of the tube.
 15. The improved rotary kiln according to claim14 wherein said separate means includes at least one material conveyingelement mounted on the interior wall of the tube such that the trace ofsaid element on said wall forms an angle with the generatrix of the tubewhich is greater than the angle of repose of the material flowingthrough the tube.
 16. The improved rotary kiln according to claim 15wherein said separate means, said combined means and said one sectiontogether extend over substantially the entire length of the tube.